Traveling wave tube comprising coupled output cavity resonators



Jan. 11, 1955 L. BRUCK 2,699,519

TRAVELING WAVE TUBE COMPRISING COUPLED OUTPUT CAVITY RESONATORS Filed Oct. 6, 1950 1 ZZIVENTGIQ- [or/W91: 2/600: 4,.-

United States Patent TRAVELING WAVE TUBE COMPRISING COUPLED OUTPUT CAVITY RESONATORS Lothar Briick, Paris, France, assignor to Compagnie Generale de Telegraphic Sans Fil, a corporation of France Application October 6, 1950, Serial No. 188,853

Claims priority, application France October 17, 1949 6 Claims. (Cl. 315-) The travelling wave tube provided with one ultrahigh frequency cavity resonator as output circuit possesses, in comparison with a simple travelling wave tube provided with an helix, the advantage of a higher efficiency. But the high quality factor of said cavity resonator determines a frequency band (determined by gain variations lower than 3 db) that is very narrow. By malting the coupling closer between the charge and the cavity resonator, a wider band can be obtained, but at the same time the measured impedance between the edges of the cavity resonator slot at the electronic beam side is considerably reduced. The value of said impedance determining the gain and efiiciency of the tube, said gain and efficiency is reduced if it is desired to increase the pass band.

It is known that the same conditions characterise high frequency amplifiers in radio receiving sets and in this case, in order to obtain a pass band sufficiently wide without a considerable reduction of gain, pass band filters are utilised.

According to the present invention, an analogous solution is employed in the output circuit of a helix and cavity resonator tube, notably in placing therein a pass band circuit comprised of two coupled cavity resonators. The present invention is represented as a non-limitative example in the annexed drawing, of which Figure 1 is a longitudinal section and Figure 2 an end view from the right of Figure 1.

The electronic gun C emits a beam P, which travels along the helix H following the axis. The high frequency energy enters the helix by a small antenna A1 and enters into interaction with the beam in the known manner in travelling wave tubes. At the extremity of the helix, the wave on said helix is completely absorbed by a localised attenuation L, while the beam yields its energy to a resonant cavity resonator.

According to the present invention, said output cavity resonator form a pass band circuit comprised of two cavity resonators A and B. The electronic beam yields its energy to the cavity resonator A in slot a. Cavity resonator A is coupled to cavity resonator B by slot b. In addition, Figure 1 represents the means of adjustr ment comprising screws V1, V2, V3. By turning screw V1,

elastic strip P is deformed and the width of slot b can be adjusted, therefore the coupling between A and B. The variation of the volume defined by the cavity resonators A and B due to deformation of the strip or diaphragm P in response to actuation of the screw V1 is assumed to be negligible. In this manner the width of the passing band can be regulated, and the adjustment of the load S and the passing band at the optimum efficiency of the tube. The load S is coupled by loop E to cavity resonator B.

Slot a represents the capacity of cavity resonator A, of which the variation changes the frequency of A. Screw V2, supported by strap T, is provided for tuning cavity resonator A to the desired frequency. The

2,699,519 Patented Jan. 11, 1955 resonance frequency of B can be tuned by the elements R controlled by screws V3.

The advantage of the present invention is a wider pass band than that which can be obtained with a single cavity resonator, without having the efiiciency considerably reduced as a consequence. Due to the steepness of the sides of the response curve of the filter, the disturbing frequencies are more effectively suppressed than by the use of a single cavity resonator.

I claim:

1. In a travelling wave tube including a source of an electronic beam propagated parallel to a delay line coupled with an output circuit for ultra-high frequency energy, said output circuit comprising first and second cavity resonators, means coupling said resonators in succession so as to form a pass band circuit, the first of said cavity resonators comprising a first slot located in the close proximity of the electronic beam, said means comprising a second slot remote from said beam and common to both said cavity resonators whereby said second cavity resonator is coupled with said first cavity resonator without being directly coupled with said beam, and said second cavity resonator being coupled with means for extracting energy from the tube.

2. A tube according to claim 1 in which means controlled externally of said tube and of said cavity resonators are provided to adjust independently the tuning of the two cavity resonators and the coupling therebetween.

3. A tube according to claim 1 in which the two cavity resonators have the shape of coaxial symmetrical bodies of revolution one surrounding the other, the common axis of said cavity resonators being the axis of the delay line of said tube.

4. A tube according to claim 3 in which the two cavity resonators are cylindrical sleeves comprising a common cylindrical wall, limited by flat common walls perpendicular to the axis of the delay line, one of said flat Walls being deformable.

5. A tube according to claim 4, said first slot being provided in the form of a circular gap in a cylindrical inner wall of said first cavity resonator defined by reentrant elements mounted respectively on said flat com mon walls, said second slot being provided in said common cylindrical wall, and means controlled externally of the tube being provided for adjusting independently the tuning of both said cavity resonators and the coupling therebetween.

6. A tube according to claim 5 wherein said adjusting means comprise a first screw acting on said deformable wall to adjust the width of said first slot thereby to vary the coupling between said cavity resonators, a second screw acting on said deformable wall to adjust the width of said gap and tune said first cavity resonator, and a third screw having an axially movable element mounted thereon and penetrating into said second cavity resonator to adjust the tuning thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,367,295 Llewellyn Jan. 16, 1945 2,511,407 Kleen et a1. June 13, 1950 2,575,383 Field Nov. 20, 1951 2,580,007 Dohler et a1 ]Dec. 25, 1951 2,637,001 Pierce Apr. 28, 1953 OTHER REFERENCES Article by Warnecke et al., pp. 648 649, Comptes Rendus des seances de LAcademie des Sciences, L229, Oct. 3, 1949. 

